In the related art, an auto-leveling control has been proposed in which an optical axis position of a vehicle headlamp is automatically adjusted according to a tilt angle of a vehicle to change an irradiation direction. Generally, in the auto-leveling control, a vehicle height sensor is used as a tilt detection device of the vehicle. The optical axis position of the headlamp is adjusted based on a pitch angle of the vehicle detected by the vehicle height sensor. In this regard, in JP-A-2000-085459, JP-A-2004-314856, JP-A-2001-341578 and JP-A-2009-126268, a configuration is disclosed in which an acceleration sensor is used as a tilt detection device to perform an auto-leveling control.
In a case where the acceleration sensor is used as the tilt detection device, it is possible to provide an auto-leveling system with a lightweight at a low cost, compared with the case where the vehicle height sensor is used. However, there is a demand that the auto-leveling control should be performed with high accuracy by suppressing an accuracy decrease due to detection errors of the sensor or the like.